48 
SELECTED ARTICLES. 
much oxygen as the base. A combination of resin of copaiba 
and oxide of lead, in which the proportions of oxygen are as 
4 to 1, would contain by calculation 26.56 oxide of lead, and 
73.44 of resin. The proportion of resin in the specimens sub- 
jected to analysis, is therefore a little less. This difference 
arises from the fact, that an alcoholic solution of the acetate of 
lead always lets fall a precipitate of carbonate of lead, when it 
is not perfectly protected from the action of the air. 
The combination of this same resin, with lime, gave an 
analysis: 
Lime, 8.32 
Resin, 91.68 
This combination presented an analogous composition to the 
last. The oxygen of the base being only a fourth of that con- 
tained in the resin. By calculation, a similar combination of 
resin of copaiba and lime would contain 8.45 per 100 of lime, 
and 91.55 per 100 of resin. 
As the three combinations of resin of copaiba with oxide of 
silver, oxide of lead and lime, have an analogous composition, it 
results that this resin seems to form a series of saline combina- 
tions with bases, in which the proportion of oxygen in the re- 
sin is four times as much as that of the base. It would hence ap- 
pear that the atomic weight of the resin is four times greater than 
that indicated in the formula before given. The true formula, 
therefore, is not 10 C + 16 H + 0, but 40 C + 64 H + 40 0. 
M. Rose thinks that it is rational, and perhaps more rigorously 
correct, to transform this as follows: 4(10 C + 16 H)+4 0. 
Crystallisable Resin of Colophane. — This resin was ob- 
tained in a crystalline form by Ries and Unverdorben. 
The latter, especially, has carefully described its preparation, 
its properties, and its combinations. As it enjoys all the pro- 
perties of an acid, he named it sylvic acid. M. Berzelius 
designates it as resin b of turpentine, whilst he marks the less 
crystallisable resin found in the same substance as a. 
Mr. Rose was unable to obtain crystals of this resin suffi- 
ciently well defined to determine their form; what he pro- 
